Fourth generation (4G) cellular networks employing newer radio access technology (RAT) systems that implement the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and LTE Advanced (LTE-A) standards are rapidly being developed and deployed within the United States and abroad. Many different types of 4G LTE-compliant communication devices have been introduced into the consumer electronic device marketplace. Some LTE/LTE-A wireless networks offer high data services and packetized voice service, e.g., voice over LTE (VoLTE). Some 4G wireless communication devices are capable of communicating within heterogeneous telecommunication networks that employ a diverse mixture of 4G, third generation (3G), and second generation (2G) RAT systems. Accordingly, these multi-mode communication devices are configured with radio frequency (RF) circuitry that allows the devices to readily transition between LTE/LTE-A network cells, as well as to roam amongst and transition between various 3G and 2G legacy network cells. By way of example, 3G legacy RATs may include Universal Mobile Telecommunications System (UMTS)/High Speed Packet Access (HSPA) and Code Division Multiple Access (CDMA) 2000/1× Evolution-Data Only (1× EV-DO) systems, whereas 2G legacy RATs can include Global System for Mobile Communications (GSM)/Enhanced Data Rate for GSM Evolution (EDGE) systems.
Additionally, 4G multi-mode communication devices can be configured to perform different voice calling functions using a packet-based VoLTE communication protocol or a circuit-switched 3G or 2G legacy communication protocol. The choice of which voice communication protocol the mobile device uses depends on what RATs are available to the device at its present network location. For instance, when a multi-mode communication device operates within a coverage area of an LTE/LTE-A network cell, the device can be configured to initiate a voice call using a VoLTE communications protocol, when the LTE/LTE-A network cell supports VoLTE calls. In another scenario, when the same device operates within a coverage area of a 3G or 2G legacy network cell and LTE network access is otherwise unavailable, the multi-mode communication device may be configured to initiate a voice call using a legacy circuit-switched communications protocol, such as through a 3G or 2G legacy network cell.
Generally, multi-mode communication devices are configured to prefer communication via 4G LTE networks offering relatively high data-rate throughput, as opposed to, communication via 3G or 2G legacy wireless networks that offer substantially lower data-rate throughput. For voice connections, however, higher data-rates may not be necessary as voice calls are typically low-bandwidth, periodic communications. Accordingly, in certain scenarios, such as when an LTE/LTE-A network cell may be providing a lower quality channel or experiencing congested network conditions, it may be more efficient for a mobile device to establish a voice call using a network cell with reliable radio coverage at the device's present location, as opposed to establishing the voice call using a network cell that employs a 4G RAT (offering a higher data-rate throughput) but has less reliable radio coverage at the device's current location. This scenario may exist when a multi-mode communication device operates within, or is moving into, a cell edge region of an LTE network cell, where one or more overlapping 3G or 2G network cell(s) can offer the multi-mode communication device more reliable voice service.
Accordingly, there is a need for selecting different network modes of operation for a wireless communication device to provide for stable voice communications via VoLTE-compliant LTE/LTE-A networks or legacy 3G/2G wireless networks based on network conditions in which the wireless communication device operates.